Compressively stressed laminated glass article via photosensitive glass and method of making the article

ABSTRACT

Laminated articles comprised of glass core and clad layers, more specifically, to compressively stressed laminated articles comprising a glass core sandwiched between first and second clad layers, the clad layers being formed from photosensitive glass.

This application is a divisional of U.S. application Ser. No. 14/432,560filed on Mar. 31, 2015, which claims the benefit of priority under 35U.S.C. § 371 of International Application No. PCT/US2013/063408, filedon Oct. 4, 2013, which claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application No. 61/744,854, filed on Oct. 4,2012, the content of each of which is relied upon and incorporatedherein by reference in its entirety.

BACKGROUND Field

The present specification generally relates to articles comprised ofglass core and clad layers, more specifically, to laminated articlescomprising a glass core sandwiched between first and second glass cladlayers, the clad layers being formed from photosensitive glass.

Technical Background

Glass articles, such as cover glasses, glass backplanes and the like,are employed in both consumer and commercial electronic devices such asLCD and LED displays, computer monitors, automated teller machines(ATMs) and the like. Some of these glass articles may include “touch”functionality which necessitates that the glass article be contacted byvarious objects including a user's fingers and/or stylus devices and, assuch, the glass must be sufficiently robust to endure regular contactwithout damage. Moreover, such glass articles may also be incorporatedin portable electronic devices, such as mobile telephones, personalmedia players, and tablet computers. The glass articles incorporated inthese devices may be susceptible to damage during transport and/or useof the associated device. Accordingly, glass articles used in electronicdevices may require enhanced strength to be able to withstand not onlyroutine “touch” contact from actual use, but also incidental contact andimpacts which may occur when the device is being transported.

SUMMARY

According to the present disclosure, a method for forming a laminatedglass article from a glass core layer and directly adjacent glass cladlayers formed from one or more photosensitive glass compositions.

In some embodiments, a method is disclosed comprising forming, with thefusion lamination process, a laminate glass sheet having at least onecladding layer formed from a photosensitive glass composition which isadjacent to a core layer formed from a glass composition, which in someembodiments, is not a photosensitive glass composition. After fusiondraw of the laminate structure comprised of the core and claddinglayers, the laminate structure is then exposed to UV light, sufficientto cause nucleation within the photosensitive composition, therebygrowing a secondary crystal phase within that cladding layer whichresults in compressively stressing the clad layer, and strengthening thelaminated glass structure.

In another set of embodiments, a laminated glass article formed from theabove method is also disclosed herein. In some embodiments, the coreglass has a first surface and a second surface opposite the firstsurface, where the first glass cladding layer is fused to the firstsurface of the glass core layer and a second glass cladding layer isfused to the second surface of the glass core layer. In otherembodiments, a first diffusive glass layer is disposed between the glasscore layer and the first glass cladding layer; additionally a seconddiffusive glass layer is disposed between the glass core layer and thesecond glass cladding layer; these diffusive layers is formed during,for example, the fusion forming process, or in one or more post-fusionUV light treatment steps.

Additional features and advantages of the glass compositions and glassarticles formed from the glass compositions will be set forth in thedetailed description which follows, and in part will be readily apparentto those skilled in the art from that description or recognized bypracticing the embodiments described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments and areintended to provide an overview or framework for understanding thenature and character of the claimed subject matter. The accompanyingdrawings are included to provide a further understanding of the variousembodiments, and are incorporated into and constitute a part of thisspecification. The drawings illustrate the various embodiments describedherein, and together with the description serve to explain theprinciples and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a cross section of a laminated glassarticle according to one or more embodiments shown and described herein;and

FIG. 2 schematically depicts a fusion draw process for making the glassarticle of FIG. 1.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of glass-ceramiccompositions disclosed herein and articles incorporating the same,examples of which are illustrated in the accompanying drawings. Wheneverpossible, the same reference numerals will be used throughout thedrawings to refer to the same or like parts.

The term “liquidus viscosity,” as used herein, refers to the shearviscosity of the glass composition at its liquidus temperature.

The term “liquidus temperatures,” as used herein, refers to the highesttemperature at which devitrification occurs in the glass composition

The term “CTE,” as used herein, refers to the coefficient of thermalexpansion of the glass composition averaged over a temperature rangefrom about 20° C. to about 300° C.

The term “substantially free,” when used to described the absence of aparticular oxide component in a glass composition, means that thecomponent is present in the glass composition as a contaminant in atrace amount of less than 1 mol. %.

In the embodiments of the glass compositions described herein, theconcentration of constituent components (e.g., SiO₂, Al₂O₃, Na₂O and thelike) are given in mole percent (mol. %) on an oxide basis, unlessotherwise specified.

The glass compositions described herein may optionally include one ormore fining agents. The fining agents may include, for example, SnO₂,As₂O₃, Sb₂O₃ and combinations thereof. The fining agents may be presentin the glass compositions in an amount greater than or equal to about 0mol. % and less than or equal to about 0.5 mol. %. In exemplaryembodiments, the fining agent is SnO₂. In these embodiments, SnO₂ may bepresent in the glass composition in a concentration which is greaterthan about 0 mol. % and less than or equal to about 0.2 mol. % or evenless than or equal to about 0.15 mol. %.

In some embodiments described herein, the glass compositions may furthercomprise trace amounts of other oxides.

In some embodiments described herein, the glass compositions aresubstantially free of heavy metals and compounds containing heavymetals. Glass compositions which are substantially free from heavymetals and compounds containing heavy metals may also be referred to as“SuperGreen” glass compositions. The term “heavy metals,” as usedherein, refers to Ba, As, Sb, Cd, and Pb.

The glass compositions disclosed herein have a liquidus viscosity whichrenders them suitable for use in a fusion draw process and, inparticular, for use as a glass cladding composition or a glass corecomposition in a fusion laminate process.

Referring now to FIG. 1, the glass compositions described herein may beused to form an article, such as the laminated glass article 100schematically depicted in cross section in FIG. 1. The laminated glassarticle 100 generally comprises a glass core layer 102 and a pair ofglass cladding layers 104 a, 104 b. The glass compositions describedherein are particularly well suited for use as the glass claddingslayers, as will be discussed in more detail herein.

FIG. 1 illustrates the glass core layer 102 shown comprising a firstsurface 103 a and a second surface 103 b which is opposed to the firstsurface 103 a. A first glass cladding layer 104 a is fused directly tothe first surface 103 a of the glass core layer 102 and a second glasscladding layer 104 b is fused directly to the second surface 103 b ofthe glass core layer 102. Post-ceramming, the glass cladding layers 104a, 104 b are fused to the glass core layer 102 without any additionalmaterials, such as adhesives, polymer layers, coating layers or thelike, being disposed between the glass core layer 102 and the glasscladding layers 104 a, 104 b. Thus, a first surface of the glass corelayer is directly adjacent the first glass cladding layer, and a secondsurface of the glass core layer is directly adjacent the second glasscladding layer. In some embodiments, the glass core layer 102 and theglass cladding layers 104 a, 104 b are formed via a fusion laminationprocess. Diffusive layers (not shown) may form between the glass corelayer 102 and the glass cladding layer 104 a, or between the glass corelayer 102 and the glass cladding layer 104 b, or both.

In at least some of the embodiments of the laminated glass article 100described herein, the glass cladding layers 104 a, 104 b are formed froma first glass-ceramic composition having an average cladding coefficientof thermal expansion CTE_(clad) and the glass core layer 102 is formedfrom a second, different glass composition which has an averagecoefficient of thermal expansion CTE_(core).

Specifically, the glass articles 100 described herein may be formed by afusion lamination process such as the process described in U.S. Pat. No.4,214,886, which is incorporated herein by reference. Referring to FIG.2 by way of example, a laminate fusion draw apparatus 200 for forming alaminated glass article includes an upper isopipe 202 which ispositioned over a lower isopipe 204. The upper isopipe 202 includes atrough 210 into which a molten glass cladding composition 206 is fedfrom a melter (not shown). Similarly, the lower isopipe 204 includes atrough 212 into which a molten glass core composition 208 is fed from amelter (not shown). In the embodiments described herein, the moltenglass core composition 208 has an appropriately high liquidus viscosityto be run over the lower isopipe 204.

As the molten glass core composition 208 fills the trough 212, itoverflows the trough 212 and flows over the outer forming surfaces 216,218 of the lower isopipe 204. The outer forming surfaces 216, 218 of thelower isopipe 204 converge at a root 220. Accordingly, the molten glasscore composition 208 flowing over the outer forming surfaces 216, 218rejoins at the root 220 of the lower isopipe 204 thereby forming a glasscore layer 102 of a laminated glass structure.

Simultaneously, the molten glass-ceramic cladding compositions 206overflows the trough 210 formed in the upper isopipe 202 and flows overouter forming surfaces 222, 224 of the upper isopipe 202. The moltenglass-ceramic cladding composition 206 has a lower liquidus viscosityrequirement to be run on the upper isopipe 202, and will have a CTEeither equal to or less than the glass core composition 208 (forexample, within about 5×10-7) when present as a glass. The moltenglass-ceramic cladding composition 206 is outwardly deflected by theupper isopipe 202 such that the molten glass cladding composition 206flows around the lower isopipe 204 and contacts the molten glass corecomposition 208 flowing over the outer forming surfaces 216, 218 of thelower isopipe, fusing to the molten glass core composition and formingpre-cerammed glass cladding layers 104 a, 104 b around the glass corelayer 102.

In some embodiments, in the laminated sheet so formed, the cladthickness will also be significantly thinner than the core glassthickness so that the clad goes into compression and the core intotension. But as the CTE difference is low, the magnitude of the tensilestress in the core will be very low (e.g on the order of 10 MPa orlower) which will allow for the production of a laminated sheet thatwill be relatively easy to cut off the draw due to its low levels ofcore tension. Sheets can thus be cut from the laminate structure orlaminated article that is drawn from the fusion draw apparatus, andafter the sheets are cut, the cut product can then be subjected to asuitable UV light treatment(s), such as to form a final laminatedarticle.

In some embodiments, the liquidus viscosity of the photosensitive glassis about 200 kP or below; in some of these embodiments, thephotosensitive glass is a high alkali (largely Li) aluminosilicateglass. The liquidus viscosity can be changed with glass components, suchas changing the ratio of alumina to alkalis or the blend of alkalis;additionally, the photosensitivity sensitivity can be changed, forexample per method used.

For example, in some embodiments the glass is exposed to UV light whichresults in nucleation by Ag and, upon heat treatment, lithium silicatecrystals are grown such as lithium metasilicate (Li2SiO3) and/or lithiumdisilicate (Li2Si2O5). In some embodiments, the CTE of the as-made glassis in the range of 70-80×10-7 C. Subjecting this glass to a second andhigher temperature, some re-crystallization occurs to form ß-spodumene,resulting in a lowered CTE, to about 60×10-7 C. In embodiments whereLi2Si2O5 persists plus silica (low-T tridymite), the CTE is higher, forexample up to about 100×10-7 C. The CTE of the as-made glass can matchthat of the inner (core) glass while being formed, but then can bechanged to form a compressive (clad) layer upon photosensitive-drivencrystallization.

Exemplary photosensitive glasses are provided in Table 1.

TABLE 1 Composition (mole %) 13 14 15 16 17 18 19 20 21 22 23 SiO2 73.576.7 74.9 74.7 73.6 73.8 74.8 72.7 72.1 71.4 70.8 Al2O3 5.0 2.8 3.7 4.54.9 4.9 5.1 4.9 4.8 4.8 4.8 Li2O 17.7 14.6 13.2 13.2 12.7 12.0 16.5 14.115.9 17.6 19.2 Na2O 1.1 1.4 1.6 1.6 2.6 2.6 1.0 2.3 2.1 1.8 1.5 K2O 1.44.1 4.3 3.9 3.2 3.8 1.3 3.5 3.0 2.5 2.1 BaO 0 0 1.2 1.2 2.5 2.5 0 2.01.4 0.9 0.5 ZnO 1.2 0.3 0.9 0.7 0.2 0.2 1.2 0.4 0.6 0.8 1.0 CeO2 0.0030.003 0.006 0.004 0.005 0.005 0.004 0.005 0.005 0.005 0.004 SnO2 0 0.0120.012 0.012 0.012 0.012 0 0.001 0.001 0.004 0.0002 Sb2O3 0.04 0.0900.120 0.109 0.106 0.107 0.040 0.092 0.079 0.067 0.055 Ag 0.050 0.0480.049 0.049 0.049 0.044 0.043 0.056 0.050 0.049 0.043 Au 0.00003 0.00030.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0-300° C.CTE 75 80.9 80.2 77.1 80.0 81.3 68.4 80.4 80.1 80.1 79.9 24 hourLiquidus 940 880 850 860 840 840 950 855 870 885 890 (° C.) Liquidus 2071 123 119 220 140 38 99 56 34 25 Viscosity (kP)

The exemplary glasses in Table 1 are also candidates for ion-exchange,even if they are not used as photosensitive material because of the highLi content. The Li can be exchanged with a Na- or K-rich inner glass toform a strengthened laminate. Such alkali migration could also occurduring the draw. Thus, in some embodiments disclosed herein, a laminatedglass article comprises a glass core layer and one or more directlyadjacent glass clad layers formed from one or more photosensitive orion-exchangeable glass compositions. The clad layer can then beprocessed to comprise photosensitized, or ion-exchanged, cladcompositions, resulting in a strengthened laminate article.

In some embodiments, the clad layer comprises from about 70.0 mol. % toabout 77.0 mol. % SiO2; from about 2.5 mol. % to about 5.0 mol. % Al2O3;from about 12.0 mol. % to about 18.0 mol. % Li2O. In some of theseembodiments, the clad layer further comprises from about 1.0 mol. % toabout 3.0 mol. % Na2O. In some of these embodiments, the clad layerfurther comprises from about 1.0 mol. % to about 5.0 mol. % K2O. In someof these embodiments, the clad layer further comprises from about 0 mol.% to about 2.5 mol. % BaO. In some of these embodiments, the clad layerfurther comprises from about 0.1 mol. % to about 1.3 mol. % K2O.

The laminated articles disclosed herein may be employed in a variety ofconsumer electronic devices including, without limitation, mobiletelephones, personal music players, tablet computers, LCD and LEDdisplays, automated teller machines and the like.

In some embodiments, the laminated article may comprise one or morelayers which are opaque, transparent or translucent, such as a cladderived from a glass composition wherein the clad layer is opaque,transparent or translucent after heat treatment(s). Furthermore, the useof glass in sheet form can be utilized.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method forming a glass ceramic sheet,comprising: forming, via fusion draw, a laminate glass sheet comprisinga cladding layer formed from a photosensitive composition and a corelayer formed from a non-photosensitive glass composition; exposing thelaminate glass sheet to UV light, sufficient to cause nucleation withinthe photosensitive composition, thereby growing a secondary crystalphase within the cladding layer, which results in compressivelystressing the cladding layer and thereby strengthening the glass sheetinto a compressively strengthened laminated glass structure.
 2. Themethod of claim 1, comprising cutting the laminate glass sheet after theforming step and before the exposing step.
 3. The method of claim 2,wherein during the cutting, the coefficient of thermal expansion (CTE)difference between the non-photosensitive glass composition and thephotosensitive composition is less than or equal to about 5×10⁻⁷/° C. 4.The method of claim 3, wherein during the cutting, the CTE of thephotosensitive composition is 70×10⁻⁷/° C. to 80×10⁻⁷/° C.
 5. The methodof claim 1, wherein: before exposing the laminate glass sheet to UVlight, a coefficient of thermal expansion (CTE) of the photosensitivecomposition is less than or equal to a CTE of the non-photosensitiveglass composition, and a difference between the CTE of thenon-photosensitive glass composition and the CTE of the photosensitivecomposition is less than or equal to about 5×10⁻⁷/° C.; and aftergrowing the secondary crystal phase within the photosensitivecomposition, the CTE of the photosensitive composition is less than orequal to the CTE of the non-photosensitive glass composition, and thedifference between the CTE of the non-photosensitive glass compositionand the CTE of the photosensitive composition is greater than about5×10⁻⁷° C.
 6. The method of claim 1, wherein the cladding layercomprises from about 70.0 mol. % to about 77.0 mol. % SiO₂, from about2.5 mol. % to about 5.0 mol. % Al₂O₃, and from about 12.0 mol. % toabout 18.0 mol. % Li₂O.
 7. The method of claim 1, wherein the claddinglayer comprises from about 1.0 mol. % to about 3.0 mol. % Na₂O.
 8. Themethod of claim 1, wherein the cladding layer comprises from about 1.0mol. % to about 5.0 mol. % K₂O.
 9. The method of claim 1, wherein thecladding layer comprises from about 0 mol. % to about 2.5 mol. % BaO.10. The method of claim 1, wherein the cladding layer comprises fromabout 0.1 mol. % to about 1.3 mol. % K₂O.
 11. The method of claim 1,wherein the cladding layer comprises beta-spodumene.
 12. The method ofclaim 1, wherein the core layer comprises K2O in a higher concentrationthan the cladding layer.
 13. The method of claim 1, comprisingexchanging Li in the cladding layer with at least one of Na or K in thecore layer.
 14. The method of claim 1, wherein: the cladding layercomprises a first cladding layer and a second cladding layer; and thecore layer is disposed between the first and second cladding layers. 15.A laminated article comprising: a glass core layer disposed between afirst glass cladding layer and a second glass cladding layer; whereinthe glass core layer has a composition which is different from thecomposition of the first and second glass cladding layers; wherein atleast one of the first glass cladding layer or the second glass claddinglayer comprises lithium silicate crystals; and wherein the lithiumsilicate crystals are lithium metasilicate (Li2SiO3), lithium disilicate(Li2Si2O5), or a combination thereof.
 16. The laminated article of claim15 wherein a coefficient of thermal expansion (CTE) of the at least oneof the first glass cladding layer or the second glass cladding layer isin the range of about 70-80×10⁻⁷/° C.
 17. The laminated article of claim15, wherein the composition of the core layer is a non-photosensitiveglass composition.
 18. A laminated article comprising: a glass corelayer disposed between a first glass cladding layer and a second glasscladding layer; wherein the glass core layer has a composition which isdifferent from the composition of the first and second glass claddinglayers; and wherein at least one of the first glass cladding layer orthe second glass cladding layer comprises beta-spodumene.
 19. Thelaminated article of claim 18 wherein a coefficient of thermal expansion(CTE) of the at least one of the first glass cladding layer or thesecond glass cladding layer is up to about 60×10⁻⁷° C.
 20. The laminatedarticle of claim 18 wherein a coefficient of thermal expansion (CTE) ofthe at least one of the first glass cladding layer or the second glasscladding layer is up to about 100×10⁻⁷° C.